Armadilloフォーラム

お世話になります。

Armadillo-X1製品マニュアルVersion2.0.0 の [12.5 C言語による開発環境] に従い、
開発用パッケージのインストールを行いたいのですが、

# sudo apt-get install libssl-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package libssl-dev

となりインストールができません。
そこでupdateをかけてみたのですが、

# sudo apt-get update
Err http://download.atmark-techno.com jessie InRelease

Err http://download.atmark-techno.com jessie Release.gpg
Could not resolve 'download.atmark-techno.com'
Err http://security.debian.org jessie/updates InRelease

Err http://security.debian.org jessie/updates Release.gpg
Could not resolve 'security.debian.org'
Err http://ftp.jp.debian.org jessie InRelease

Err http://ftp.jp.debian.org jessie Release.gpg
Could not resolve 'ftp.jp.debian.org'
Reading package lists... Done
W: Failed to fetch http://ftp.jp.debian.org/debian/dists/jessie/InRelease

W: Failed to fetch http://security.debian.org/dists/jessie/updates/InRelease

W: Failed to fetch http://download.atmark-techno.com/debian/dists/jessie/InRelease

W: Failed to fetch http://download.atmark-techno.com/debian/dists/jessie/Release.gpg Could not resolve 'download.atmark-techno.com'

W: Failed to fetch http://security.debian.org/dists/jessie/updates/Release.gpg Could not resolve 'security.debian.org'

W: Failed to fetch http://ftp.jp.debian.org/debian/dists/jessie/Release.gpg Could not resolve 'ftp.jp.debian.org'

W: Some index files failed to download. They have been ignored, or old ones used instead.

とエラーが出てしまい、完了できません。
経験不足のためうまく原因を調べられず、こちらでお力をお借りしたく思います。

以上、よろしくお願い致します。